USB, USB Hubs, Firewire 1394

My Compaq Presario SR1224NX Desktop comes with a few standard USB sockets (4 at the back, and 1 at the front panel). I have a scanner connected at one of them at the back, and also an external DVD writer at another at the back.

I have tried to insert a USB flash-drive into the one (USB) at the front, the flash-drive opens up in Windows XP (Home), but it causes my scanner to start too, ending in a conflict between the two devices (the scanner loses out with error at TWAIN, etc). No external USB Hub is used. The problem only occurs when I connect the flash-drive to the USB socket at the front panel.

(Note: The above problem arises even if I do not use any of those external USB Hubs. It is with the flash-drive inserted at the front panel socket only, and no problem inserting the flash-drive to the sockets at the back, or with any other device inserted at the front one).

Question: Can someone explain what is the problem.

Another question:
In the market are external USB Hubs (e.g. 4-port) which can be connected to an existing socket for connection for additional hardware devices. Would they cause any conflict problems ?

And one more question:
I have found an external USB Hub (4 port) with one Firewire 1394 socket too. Can the device connected to the Firewire 1394 socket operate at the top speed which the Firewire 1394 is designed to operate by itself ?

Appreciate your help. Thanks.

An external hub shouldn't cause any conflicts, they are passive devices. And the Firewire port on a hub will operate at the maximum speed.

As for the conflict, the only thing I can suggest is to swap the headers to the USB ports on the motherboard and see if it is happier with that arrangement.

External USB hubs that have their own power adapters should minimize chances of resource issues.
Compaq mobo designs can be quite finicky about resources.